More specifically, the invention relates to a vehicle seat comprising a seat portion and a backrest connected to the seat portion by at least one hinge mechanism to allow adjusting the tilt of the backrest and to lock the backrest into the selected tilt angle, the seat comprising a seat element chosen from among the backrest and the seat portion, said seat element extending along a mean plane and having two sides, and said seat element comprising:                a shell of plastic material, having two lateral edges which respectively extend along the sides of the seat element between a first end near the hinge mechanism and a second end further away from the hinge mechanism,        at least one rigid insert of composite material which is overmolded by one of the two lateral edges of the shell of plastic material, said rigid insert extending for a certain length from the first end of said corresponding lateral edge, said insert comprising resistant fibers embedded in a synthetic matrix, and said insert presenting a U-shaped cross-section having a core substantially perpendicular to the mean plane of the seat element and two side flanges substantially parallel to the mean plane of the seat element, said core being connected to said hinge mechanism at the first end of the corresponding lateral edge.        
Document US-A-2008/038569 describes an example of a seat of this type.